The term "structural shapes" is here used to refer to large elongated bodies as used in the erection of buildings, bridges and like massive steel structures and wherever steel frameworks are intended to be provided, either as a core of a concrete structure or independently thereof. Typical structural steel shapes include I-beams, H-beams, channels, angles, bars and various cross sections, and more complex steel elements which generally are rolled in rolling mills from ingots and billets, blooms or continuously cast structures.
In steel fabrication it is of importance that such structural shapes be machined, usually drilled or bored with high precision, so that the structural shapes can be assembled at the building site with bolts or rivets. Frequently other machining of the workpiece is required, e.g. to cut the structural shape to size, to mill openings or steps in flanges or webs of the structural shape, or to cut intricate patterns in the web or flange.
All of these operations have generally been carried out on separate machines or at various locations in a fabrication yard or on the building site.
It is common, for example, to drill such structural shapes in an apparatus which comprises a machine frame, a feed-roller conveyor, a discharge-roller conveyor, a mechanism or means for advancing the workpiece along the roller conveyor and through the machine frame and a measuring unit for measuring this advance, at least one raisable and lowerable boring unit on the frame for boring vertical holes. In the structural shape or workpiece, at least one horizontal boring unit movable back and forth, and a computer-controller system connected to these units and to the advancing unit or drive for effecting a drilling program for the particular workpiece.
An apparatus of this type is available in various configurations. It can be combined, for example, with a sawing machine (see DE 40 23 125 A1) or associated with a cutting-torch system for burning the structural shape in various patterns (see DE 33 31 844 C1).
In general, the earlier apparatus has been found to be highly effective.
In the preparation of structural shapes, especially heavy steel structural shapes for the erection of steel frame structures, it frequently has been found to be desirable to effect a milling operation, especially to produce windows or compartments or cutouts in the flanges or webs of the structural shape.
In the past it has been required to shift the structural shape, i.e. the workpiece, from the drilling apparatus to the milling unit or vice versa.
The milling apparatus generally did not operate with feed and discharge-roller conveyors or with the mechanisms or means for advancing structural shapes along such conveyors as were provided in the boring machine. Instead, the workpiece commonly was clamped on the work table or milling machine slide or carriage and required accurate positioning thereon.
The carriage or slide or table upon which the workpiece was clamped was generally displaced by a spindle drive or the like.
As a consequence, the operations involved in transferring the workpiece to and from the milling machine and effecting a milling operating were time-consuming, expensive and frequently inaccurate because of the comparatively large size of the workpiece and the importance of correlating the bores formed or to be formed in the workpiece with any milling which may have been required.